A newly released study from e-business performance management services provider Keynote Systems attempts to answer the question of which service among the nation's top six VoIP providers is the "best." The answer is not a straightforward one, and the study also identified a need for VoIP services to improve in order to narrow the gap with PSTN quality and reliability.

In terms of overall reliability, Keynote ranked Vonage first among the VoIP providers. Though in terms of audio clarity, AT&T CallVantage ranked first.

Keynote ranked Vonage, Primus Lingo, Verizon Voicewing, Packet 8, SkypeOut and AT&T CallVantage as part of its study. The respective services were tested on seven different networks including broadband cable from Comcast and Time Warner Cable; DSL from Verizon and SBC; business-class networks from Sprint, UUNET and AT&T.

Ranking factors
Ten factors were taken into account in Keynote's study. Included were service availability, dropped calls, listening quality, average number of call attempts to make a connection, two dealing with "MOS" (Mean Opinion Score is a formally tested subjective measure of speech quality) and three related to audio delay.

Though Keynote ranked Vonage first in terms of reliability, they noted that the "Dropped Calls" performance factor of Vonage still had room for improvement. AT&T's CallVantage also had room to improve on its leading audio clarity ranking in terms of the "geographic variability on the audio delay factor."

The choice of underlying network carrier also made a "dramatic" contribution in terms of both audio clarity and service reliability according to the Keynote study. Time Warner Cable was ranked by Keynote as the most reliable carrier.

Not up to snuff
Perhaps most surprising about the Keynote study was the conclusion that VoIP service is not yet at the same level of standards as the POTS system is in terms of user expectations. "VoIP reliability and audio clarity are important factors limiting the widespread adoption of VoIP in consumer markets," said Dharmesh Thakker senior product manager for service level solutions at Keynote. "Consumers are unsure whether VoIP can live up to the dial-tone reliability and crystal-clear communication quality they have come to expect with traditional phone service over the years."

Keynote does not stand alone on its conclusions about the VoIP quality.

Info-Tech Research Senior Analyst Carmi Levy told EnterpriseVoIPplanet.com that Info-Tech research is consistent Keynote's conclusions and that his firm is hearing the same message from its own clients.

"When IT decision makers consider moving their phone service over to VoIP, Quality of Service (QoS) is typically one of their highest-priority concerns," Levy said. "Shifting to VoIP moves us into a brand new telephony world where the possibility of not having a dial tone, and of engaging in a stuttered, lag-laden conversation is suddenly very real."

In contrast Levy argues the Plain Old Telephone Service (POTS)is almost universally crisp, clear and reliable to the point that most never need to think about it.

"As a result, it's easy to understand why decision makers are demanding improvements in quality and reliability before they comfortably commit to the new technology," Levy explained. "No one, after all, wants to implement a technology that delivers worse service than the infrastructure it replaced."

Quality of Service related concerns are not showstoppers as much as they are brakes in Levy's opinion. In his estimation both the quality and reliability issues will ultimately be addressed and VoIP will assume its place as the dominant voice communication infrastructure.

"For now, however, today's mainstream VoIP offerings are just immature enough to give decision makers pause," Levy said. "Great care is clearly called for until this settles out."